An adaptive data rate modulator/demodulator (modem) (102), particularly useful for transmitting data over fading communications channels, uses an adaptive data rate technique which supports multiple data rates in the same device. The modem incorporates an adaptive data rate encoder (104) and an adaptive data rate decoder (105) using adaptive, parallel-branch decoding to translate received symbols into corresponding data bits. Significantly, the soft decision metrics of the decoder are also used to provide an estimate W of the signal-to-noise ratio. An optional predictor (232) receives W from the adaptive data rate decoder (105) and predicts the future signal-to-noise ratio to determine the desired data rate for the modem. The data rate is changed automatically and dynamically without interrupting the decoding process. A constant channel symbol rate and a single signal set simplify signal acquisition and synchronization. Incoming and outgoing data are buffered, and the transmission rate is changed dynamically by a memory controller (109) to avert buffer overflows and underflows. An optional adaptive phase-lock loop system (116) maintains synchronization of the decoder at all data rates.
Provided with a method of performing power control in a CDMA mobile communication system, characterized by including the steps of: repeatedly updating information concerning the change of a channel state between a mobile station and a base station at regular intervals; varying a channel gain up/down time and/or a channel gain up/down delta adaptively based on the updated information; and adjusting the channel gain between the mobile station and the base station.
An audio data transmission system encodes audio files into individual audio data blocks which contain a variable number bits of digital audio data that were sampled at a selectable sample rate. The number of bits of digital data and the input sampling rate are scaleable to produce an encoded bit stream bit rate that is less than or equal to an effective operational bit rate of a recipient's modem. The audio data transmission system uses computing units which are designed to select an appropriate combination of block size and input sampling rate to maximize the available bandwidth of the receiving modem. For example, if the modem connection speed for one modem is 14.4 kbps, a version of the audio data compressed at 13000 bits/s might be sent to the recipient; if the modem connection speed for another modem is 28.8 kbps, a version of the audio data compressed at 24255 bits/s might be sent to the receiver. The audio data blocks are then transmitted at the encoded bit stream bit rate to the intended recipient's modem. The audio data blocks are decoded at the recipient to reconstruct the audio file and immediately play the audio file as it is received. The audio data transmission system can be implemented in online service systems, ITV systems, computer data network systems, and communication systems.
A digital communication system is disclosed. A transmitter combines a digitized signal into a digital data stream with variable data rate and transmits it to a receiver. The receiver decodes the received signal with an actually transmitted data rate. For this reason, the receiver has to estimate the coding data rate of the received signal. The receiver decodes the received signal at one decoding rate, which is evaluated whether the decoding rate is correct or not. Such evaluation is achieved by, for example, measuring S/N ratio. According to such estimation the receiver estimates the actual transmitted data rate.
An improved data communication technique may be employed with modems through a packet network. The disclosed technique facilitates a virtual end-to-end connection between two modems such that the two modems can effectively behave as if directly connected to each other, unaware of any modifications to the data being transferred or to the protocols configured within the communication connection. Preferably, a data communication system for carrying out the communication technique demodulates data coming from a first modem, transports the demodulated data in packets between two gateways, and then remodulates the data before delivering to a second modem at the other end. In accordance with various aspects of the present invention, various alternatives for calling and quality of service set-up mechanisms, the establishment of a communication session, the transport of data during a communication session, the flow control between all system components involved, and the mechanisms for the termination of communications are also provided.
A system and method to measure channel quality in terms of signal to noise ratio for the transmission of coded signals over fading channels. A Viterbi decoder metric for the Maximum Likelihood path is used as a channel quality measure. This Euclidean distance metric is filtered in order to smooth out short term variations. The filtered or averaged metric is a reliable channel quality measure which remains consistent across different coded modulation schemes and at different mobile speeds. The filtered metric is mapped to the signal to noise ratio per symbol using a threshold based scheme. Use of this implicit signal to noise ratio estimate is used for the mobile assisted handoff and data rate adaptation in the transmitter.
